The New Physics and Its Evolution eBook

In the establishment of these theories, the language
of ordinary optics has always been employed.
The phenomena are looked upon as due to mechanical
deformations or to movements governed by certain forces.
The electromagnetic theory leads, as we have seen,
to the employment of other images. M.H.
Poincare, and, after him, Helmholtz, have both proposed
electromagnetic theories of dispersion. On examining
things closely, it will be found that there are not,
in truth, in the two ways of regarding the problem,
two equivalent translations of exterior reality.
The electrical theory gives us to understand, much
better than the mechanical one, that in vacuo
the dispersion ought to be strictly null, and this
absence of dispersion appears to be confirmed with
extraordinary precision by astronomical observations.
Thus the observation, often repeated, and at different
times of year, proves that in the case of the star
Algol, the light of which takes at least four years
to reach us, no sensible difference in coloration
accompanies the changes in brilliancy.

Sec. 2. THE THEORY OF LORENTZ

Purely mechanical considerations have therefore failed
to give an entirely satisfactory interpretation of
the phenomena in which even the simplest relations
between matter and the ether appear. They would,
evidently, be still more insufficient if used to explain
certain effects produced on matter by light, which
could not, without grave difficulties, be attributed
to movement; for instance, the phenomena of electrification
under the influence of certain radiations, or, again,
chemical reactions such as photographic impressions.

The problem had to be approached by another road.
The electromagnetic theory was a step in advance,
but it comes to a standstill, so to speak, at the
moment when the ether penetrates into matter.
If we wish to go deeper into the inwardness of the
phenomena, we must follow, for example, Professor
Lorentz or Dr Larmor, and look with them for a mode
of representation which appears, besides, to be a natural
consequence of the fundamental ideas forming the basis
of Hertz’s experiments.

The moment we look upon a wave in the ether as an
electromagnetic wave, a molecule which emits light
ought to be considered as a kind of excitant.
We are thus led to suppose that in each radiating molecule
there are one or several electrified particles, animated
with a to-and-fro movement round their positions of
equilibrium, and these particles are certainly identical
with those electrons the existence of which we have
already admitted for so many other reasons.

In the simplest theory, we will imagine an electron
which may be displaced from its position of equilibrium
in all directions, and is, in this displacement, submitted
to attractions which communicate to it a vibration
like a pendulum. These movements are equivalent
to tiny currents, and the mobile electron, when animated
with a considerable velocity, must be sensitive to
the action of the magnet which modifies the form of
the trajectory and the value of the period. This
almost direct consequence was perceived by Lorentz,
and it led him to the new idea that radiations emitted
by a body ought to be modified by the action of a
strong electromagnet.